Quantitatively, the so-called Kennedy Round of tariff cuts was large enough to be noticed, but not earth-shaking: as this legislation was phased in, our average duty on dutiable imports fell from 14.3 percent in 1967 to 9.9 percent in 1972.

"The magnitude of the tariff shock in the Smoot-Hawley legislation, which increased the domestic price of imports by 5% at a time when dutiable imports were just 1.4% of GDP, was simply not large enough to trigger the kind of economic contraction experienced after 1930," Mr. Irwin concludes.